/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(head==nullptr)
        {
            return nullptr;
        }
        vector<int> ans;
        ListNode* cur=head;
        //1 2 3 4
        while(cur)
        {
            ans.push_back(cur->val);
            cur=cur->next;
        }
        reverse(ans.begin(), ans.end());
        cur=head;
        for(int i=0;i<ans.size();i++)
        {
            cur->val=ans[i];
            cur=cur->next;
        }      
        return head;
    }
};